1. Field of the Invention
The present invention relates generally to substrate processing reactors, and more particularly to rapid thermal process reactors with a low profile dome.
2. Description of Related Art
FIG. 1 is a simplified cross-sectional view of RTP reactor 100 for processing one or more semiconductor substrates, e.g., substrates 111, 112. Reactor 100 included vessel 101, susceptor 102, susceptor support 104, radiant heat source 110 (including a plurality of lamps 105 and reflectors 106), passive heat distribution element 107, side inject gas jets 114a, 114b and gas exhaust pipes 109a, 109b. 
Vessel 101 was formed by bottom wall 101a, sidewall 101b and domed top wall 101c. Walls 101a, 101b and 101c bounded reaction chamber 103. Bottom wall 101a and sidewall 101b were made of stainless steel and lined with quartz. In one embodiment, bottom wall 101a was circular and sidewall 101b was cylindrical. Dome-shaped top wall 101c was made of quartz so that relatively little of the radiant energy from radiant heat source 110 was absorbed by top wall 101c. Thus, the radiant energy passed through top wall 101c unimpeded to directly heat substrates 111, 112.
The shape of top wall 101c was chosen as a compromise between several factors. As top wall 101c was made increasingly flat, the possibility increased that top wall 101c would collapse when reaction chamber 103 was held at a vacuum pressure, i.e., less than 100 torrs, for instance, during a reduced pressure BICMOS process.
On the other hand, as the curvature of top wall 101c was increased, radiant heat source 110 was moved increasingly further away from substrates 111, 112. Thus, a greater energy output from radiant heat source 110 was required to maintain a given temperature of substrates 111, 112.
Additionally, as the curvature of top wall 101c increased, the distance of top wall 101c from substrates 111, 112 also increased so that at least some portion of the process gases had a longer distance to descend. This portion of the process gases had a longer time to heat up before the gases were deposited on substrates 111, 112. Thus, the vertical temperature distribution of the process gases was not uniform across the reaction chamber. The curvature of top wall 101c also affected the flow of the process gases as they descended upon substrates 111, 112.
The exact shape of top wall 101c was empirically determined by testing a number of different shapes and one was chosen that yielded a desired combination of the above-identified characteristics. Upper wall 101c had a cross-sectional shape that formed an approximately circular arc. Top wall 101c had a characteristic height h between 3″ and 6″ inclusive.
Gas-deflecting shelf 173 sat on a quartz liner that was adjacent to side wall 101b in reaction chamber 103. Gas-deflecting shelf 173 was made of, for instance, quartz so that gas-deflecting shelf 173 disturbed the temperature distribution within susceptor 102 and the substrate or substrates as little as possible.
Gas-deflecting shelf 173 forced gases that might otherwise have passed between susceptor 102 and side wall 101b of the reactor to flow over surface 102a of susceptor 102 (and, thus, the substrate or substrates), when susceptor 102 was in the processing position as shown by the dashed lines in FIG. 1. Gas-deflecting shelf 173 also caused an increase in velocity of gases near the edge of susceptor 102 because a smaller opening existed between susceptor 102 and gas-deflecting shelf 173 than would exist between susceptor 102 and reactor sidewall 101b if gas-deflecting shelf 173 were not present. The length of gas-deflecting shelf 173 was varied to create an opening between gas-deflecting shelf 173 and susceptor 102 so as to obtain a gas flow that yielded the desired process uniformities.
Substrates 111, 112 (FIG. 1A) were mounted on circular susceptor 102 within reaction chamber 103. Susceptor 102, susceptor support 104 and passive heat distribution element 107 are shown in the loading position in FIG. 1. Substrates 111, 112 were placed into and removed from reaction chamber 103 by one of a robot or a substrate handling system (not shown) through a door formed in sidewall 101b. The loading position was chosen to allow the robot or substrate handling system to easily extend into reaction chamber 103 and place substrates 111, 112 on susceptor 102.
When susceptor 102 was in the loading position, pins (not shown) extend through corresponding holes formed in susceptor 102 to raise substrates 111, 112 above surface 102a. Alternatively, the pins extended through holes in susceptor 102 to raise a substrate surround ring upon which substrates 111, 112 rested. Any number of pins could be used to raise each substrate 111, 112 or substrate surround ring, though at least three were desirable to stably support a substrate, e.g., substrate 111, or substrate surround ring. For example one to eight pins are used. Since it was also generally desirable to minimize the number of pins used to minimize mechanical complexity, three pins, located 120° apart in the radial direction around susceptor 102, were used to support 125 mm (5 inches), 150 mm (6 inches) and 200 mm (8 inches) substrates, and four pins, located 90° apart, were used to support 250 mm (10 inches) and 100 mm (12 inches) substrates.
In one example, substrates 111, 112 were heated by a single heat source: radiant heat source 110. Radiant heat source 110 included plurality of lamps 105 that emitted radiant energy having a wavelength in the range of less than 1 μm to about 500 μm, preferably in the range of less than 1 μm to about 10 μm, and most preferably less than 1 μm. A plurality of reflectors 106, one reflector adjacent each lamp, reflected radiant energy toward substrates 111, 112.
Radiant heat source 110 was both water-cooled and forced-air cooled. The combination of water-cooling and forced-air cooling kept lamps 105 and reflectors 106 within the required operating temperature range.
In reactor 100 (FIG. 1), passive heat distribution element 107 was mounted beneath susceptor 102 in proximity to susceptor 102. As used herein, “proximity” means as close as possible considering the limitations imposed by the physical space requirement for connecting susceptor 102 to susceptor support 104. Passive heat distribution element 107 minimized heat losses from susceptor 102, which, in turn, minimized heat losses from substrates 111, 112. Passive heat distribution element 107 was preferably made of a material that either absorbs and re-radiates heat toward susceptor 102, or that reflected heat toward susceptor 102.